1. Field of the Invention
The present invention generally relates to a method and compound for the treatment of cancer. More particularly, an embodiment relates to the use of DNA interactive compounds that bind to DNA and undergo a series of chemical reactions in the presence of DNA to generate reactive intermediates that cleave DNA.
2. Brief Description of the Related Art
In 1972 Robert Bergman and co-workers demonstrated the gas-phase thermal rearrangement of substituted 3-hexene-1,5-diynes and proposed the intermediacy of a 1,4-didehydrobenzene, in this process (Jones and Bergman, 1972). Indirect evidence for the existence of a singlet 1,4-didehydrobenzene intermediate was provided by solution-phase CIDNP experiments, which afforded the substituted benzene products (Lockhart and Bergman, 1981). Bergman""s original finding has gained additional significance in light of the discovery of an entire class of antitumor antibiotics, exemplified by calicheamicin xcex31I (Lee, 1987) that exert their potent cytotoxic effects through a Bergman cyclization of an enediyne core to produce a 1,4-didehydrobenzene intermediate. This diradical abstracts hydrogen atoms from the DNA ribose backbone, resulting in DNA strand scission (Hangeland, 1992).
Although simple, acyclic enediynes generally require higher temperatures than is physiologically relevant for Bergman cyclization to take place, synthetic enediynes that are strained may cyclize and produce DNA cleaving diradicals under physiological conditions, (Nicolaou, Dai, Tsay, Estevez, and Wrasidlo, 1992) and large numbers of these reactive enediynes have been designed, synthesized, and evaluated for biological activity (Grissom, Gunawardena, Klingberg, and Huang, 1996). More recently, the synthetic utility of the Bergman cyclization has been explored, principally by Grissom, who has employed the 1,4-didehydrobenzene intermediates afforded by the Bergman cyclization of substituted 3-hexene-1,5-diynes and substituted 1,2-diethynylbenzenes in subsequent free radical reactions to rapidly construct polycyclic compounds (Grissom, Calkins, Huang, and McMillen, 1994).
A related diradical-generating cyclization of 1,2,4-triene-5-ynes, modeled on the presumed DNA strand scission chemistry of the neocarzinostatin chromophore (Edo, 1985), has been discovered by Myers and co-workers (Myers, 1989). These workers found that eneyne allene undergoes an exothermic conversion to the xcex1,3-didehydrotoluene intermediate, which may either abstract hydrogen atoms from 1,4-cyclohexadiene to produce toluene or combine with the cyclohexyldienyl radical to form the adduct. This Myers cyclization has been exploited by many workers in the design of simple diradical-generating compounds with demonstrable ability to cleave DNA under physiological conditions (Nicolaou, Maligres, Shin and Deleon, 1990). The Myers cyclization has also been employed synthetically by Grissom (Grissom, Klingberg, Huang, and Slattery, 1997) and Wang (Wang, Wang, Tarli, and Gannet, 1996) in the construction of polycyclic molecules.
Schmittel and co-workers, (Schmittel, et al., 1995) and others (Gillman, et al., 1995) have reported anomalous products, of thermal cyclizations of enyne allenes. These products are more pronounced in cases where the enyne allene substituents R, R1, or R2 are large. In these cases, the enyne allenes undergo cyclization to the benzofulvalene biradical intermediate, the fate of which is dependent upon the nature of the substituents. Schmittel has demonstrated that enyne allenes that undergo this C2-C6 cyclization reaction are able to cleave DNA, presumably as a result of hydrogen atom abstraction by the diradical intermediate (Schmittel, Maywald, and Strittmatter, 1997).
Despite the promise, both synthetic and biological, of the chemistry of enediynes and enyne allenes, heteroatom substituted variants of these systems have not been extensively explored. Moore (Moore, 1992) has found that the enyne ketenes, generated from thermolysis of cyclobutenones, afford quinones, through the intermediate diradicals. These cyclobutenones also exhibit DNA cleaving ability, presumably due to the ability of the diradical intermediates to abstract hydrogen atoms from the DNA backbone (Sullivan, 1994). Padwa (Padwa, 1993) and Nakatani (Nakatani, 1994) have used alternative routes to enyne ketenes, which were also found to afford cycloaromatized products through diradical intermediates.
In contrast to the oxo-substituted enyne allene system, few aza-substituted enediyne or enyne allenes had been reported prior to our work. Wang and co-workers had reported the failed attempt to coax nitrile () to undergo an aza-Myers cyclization (Wang, Wang, and Sattsangi, 1996). Gillman and co-workers had reported similar findings for a related 2-allenyl cyanobenzene (Gillman and Heckhoff, 1996). Most recently, Wang and co-workers have shown that the ketenimine gives products predicted by both an aza-Myers cyclization and the C2-C6 cyclization (Shi and Wang, 1998).
The synthesis and utility of novel aza-derivatives of enediynes, enyne allenes, and diallenes is described herein. The term xe2x80x9caza-derivativexe2x80x9d is herein taken to mean aza-enediynes, aza-enyne allenes, and aza-diallenes. These aza-derivatives have the potential to generate novel reactive intermediates, and thus serve as an important tool in the study of these intermediates. In addition, these same intermediates may be harnessed to affect nucleic acid strand scission, and thus serve as the warhead of a new class of antitumor or antiviral compounds.
Aza-enediyne derivatives, in one embodiment, have the general structure: 
The parent structure includes an imine covalently coupled to two alkynyl groups. A variety of substitutents may be attached to the parent structure at the R positions. Any commonly known substituent may be placed upon the parent structure as long as the resulting compound is relatively stable.
The parent structure may also be formed as an iminium ion (i.e., a salt of the parent structure) having the structure: 
A variety of substitutents may be attached to the parent structure at the R positions. Any commonly known substituents may be placed upon the parent structure as long as the resulting compound is relatively stable. The nitrogen atom is either protonated, alkylated, or incorporated into a ring system.
Aza-enediyne derivatives, in another embodiment, have the isomeric parent structures: 
Each of the isomeric parent structures includes an imine covalently coupled to an alkynyl group and a propargyl group. The groups may be attached to either the nitrogen or the carbon as depicted above. A variety of substituents may be attached to the parent structure at the R positions. Any commonly known substituent may be placed upon the parent structure as long as the resulting compound is relatively stable.
The parent structures may also be formed as an iminium ion (i.e., a salt of the parent structure) having the structures: 
A variety of substituents may be attached to the parent structures at the R positions. Any commonly known substituents may be placed upon the parent structure as long as the resulting compound is relatively stable. The nitrogen atom is either protonated, alkylated, or incorporated into a ring system.
Aza-enyne allene derivatives, in one embodiment, have the isomeric parent structures: 
Each of the isomeric parent structures includes an imine covalently coupled to an alkynyl group and an allenyl group. The groups may be attached to either the nitrogen or the carbon as depicted above. A variety of substituents may be attached to the parent structure at the R positions. Any commonly known substituent may be placed upon the parent structure as long as the resulting compound is relatively stable.
The parent structures may also be formed as an iminium ion (i.e., a salt of the parent structure) having the structures: 
A variety of substituents may be attached to the parent structures at the R positions. Any commonly known substituents may be placed upon the parent structure as long as the resulting compound is relatively stable. The nitrogen atom is either protonated, alkylated, or incorporated into a ring system.
Aza-diallene derivatives, in one embodiment, have the general structure: 
The parent structure includes an imine covalently coupled to two allene groups. A variety of substitutents may be attached to the parent structure at the R positions. Any commonly known substituent may be placed upon the parent structure as long as the resulting compound is relatively stable.
The parent structure may also be formed as an iminium ion (i.e., a salt of the parent structure) having the structure: 
A variety of substituents may be attached to the parent structure at the R positions. Any commonly known substituents may be placed upon the parent structure as long as the resulting compound is relatively stable. The nitrogen atom is either protonated, alkylated, or incorporated into a ring system.
In another embodiment, oligomeric aza-derivatives are compounds having a dimeric or oligomeric structure composed of aza-derivatives as defined above. Any of the R substitutents R1, R2, R3, or R4, may be used to link these compounds together. xe2x80x9cDimericxe2x80x9d structures refer to compounds in which two similar structures are joined together. xe2x80x9cOligomericxe2x80x9d structures refers to compounds, on which two or more compounds having similar or different structures, are linked together. The individual aza-derivatives may be linked together by a linking group.
The aza-derivatives may be used in the treatment of cancer and other proliferative diseases. In addition, these aza-derivatives may have uses in other disease states, such as viral and bacterial infections. These aza-derivatives may be used as fluorescent dyes, and by virtue of the diradical chemistry that they enter into, they may have utility in the manufacture of dye-fast fluorescent materials such as plastics and as biochemical probes for such techniques as FISH and flow cytometry. Also by virtue of the diradical intermediates that these aza-derivatives produce under very mild conditions, they may find utility as initiators of radical reactions, including polymerization reactions.
Where clinical application of aza-derivatives is undertaken, it will be necessary to prepare the complex as a pharmaceutical composition appropriate for the intended application.
Generally, the synthesis of the aza-derivatives is accomplished by reacting an imine with an electrophilic compound. The imines may be formed by reacting a carbonyl compound (e.g., a ketone or aldehyde) with a nucleophilic amine derivative. The reaction of a carbonyl with a nucleophilic amine may also be used to produce the aza-derivatives which are iminium salts.
The compounds are believed to show cytotoxic effects by cleaving nucleic acids. When a nucleic acid is treated with an aza-derivative the interaction of the nucleic acid with the aza-derivative may cause the derivative to undergo an aza-Bergman type reaction. The aza-Bergman reaction is believed to produce a diradical species. This diradical species is believed to interact with the nucleic acid causing cleavage of the nucleic acid strands. This mechanism of action may be useful in the treatment of cancer, viral infections or bacterial infections.
Other and further aspects, features, benefits, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention given for the purpose of disclosure.